1. Field of the Invention
The present invention relates to a heat exchanger provided in an air conditioner, wherein a number of fins are juxtaposed with narrow intervals, heat exchange pipes are provided to penetrate the fins, and end portions of the heat exchange pipes projecting sideways from the outermost ones of the fins are connected by U-bend portions, thereby forming passageways.
2. Description of the Related Art
Published Unexamined Japanese Patent Application (PUJPA) No. 2-106228, for example, discloses a method of manufacturing a bent-type heat exchanger having an upper heat exchanger unit and a lower heat exchanger unit which are bent a predetermined angle at the connection portions of the fins.
According to this manufacturing method, a number of fins, each having a notch and a hole so as to have at least two connecting portions, are arranged at regular intervals. Heat conduction pipes penetrate the fins, and the notch and hole are cut off.
The connecting portions are formed as spaces. The lower end face of the upper heat exchanger unit and the upper end face of the lower heat exchanger unit are opposed to each other such that the distance therebetween is large on the outside of the bent portion and gradually decreases towards the inside of the bent portion.
If the above bent-type heat exchanger is used within the indoor unit of an air conditioner, the space for installation of the unit body is not increased, as compared to a conventional flat vertical type heat exchanger, and the heat exchange area is increased remarkably. As a result, the heat exchange efficiency is enhanced.
However, the following drawbacks reside in the above method.
The heat exchanger is provided with a front passageway and a rear passageway on the upstream side and down stream side of guided heat exchange air. First, a refrigerant or a heat exchange medium is guided into the front passageway, and then the refrigerant is guided into the rear passageway.
In the above-mentioned connecting portions, a connection pipe is passed between the front passageway of the upper and lower heat exchanger units, and the refrigerant is guided to the heat exchanger units. On the other hand, the rear passageway is connected to a refrigerant output unit from which the refrigerant which has completed heat exchange is output.
The upstream-side distance between the connecting portions is large and the downstream-side distance is small. Thus, the heat exchange air guided to the connecting portions is not subjected to heat exchange with the upstream-side front passageways, but only with the downstream-side rear passageways.
However, the refrigerant at the rear passageways is just about to be output to the refrigerant output unit and is in the super-heat state. Therefore, the refrigerant does not perform a heat exchange function.
In particular, under the conditions of high humidity, the humidity in the heat exchange air passing in the vicinity of the connecting portions is not removed.
Consequently, humid air tends to remain in the housing of the unit, and dew condensation may occur on parts of the air blower situated within the housing and on the inside wall of the housing.
In addition, in order to pass the refrigerant more smoothly and efficiently, a three-way bend is provided midway along the passageway, thereby increasing the number of passageways and optimizing the use of the passageways.
For example, when the refrigerant is distributed by the three-way bend unit in the vicinity of a refrigerant input unit in the cooling mode, the distributed refrigerant is in the liquid phase. Thus, even if the refrigerant is distributed in any manner, it is distributed substantially equally into two mutually perpendicular directions, and no problem will occur.
However, there is a case of using a three-way bend unit on the downstream side of the middle portion of the passageway, which takes in the refrigerant from a side port and distributes it in upward and downward directions.
In the vicinity of the middle portion of the passageway, a heat exchange function is performed and the ratio of gas-phase refrigerant to liquid-phase refrigerant increases. Consequently, a great amount of gas-phase refrigerant flows upwards and only a small amount of liquid-phase refrigerant flows downwards.
As a result, the amount of circulated refrigerant decreases, and the heat exchange efficiency is degraded.
Furthermore, the diameter of each heat exchange pipe used in the heat exchanger is very small (e.g. 6.35 m/m.phi.).
In the heating mode, the heat exchanger of the indoor unit functions as a higher-pressure side heat exchanger, and the flow rate of the refrigerant increases. Thus, the heat exchange efficiency is enhanced.
However, in the cooling mode, this heat exchanger functions as a lower-pressure side heat exchanger. Thus, a pressure loss of refrigerant due to pipe friction increases considerably and the cooling performance decreases.
In order to compensate the decrease in cooling performance, it can be thought to branch the passageway in front of the heat exchanger and decrease the pressure loss in the heat exchanger. However, it is difficult to uniformly supply the refrigerant to the branched passageways, and the heat exchange efficiency deteriorates due to the non-uniform flow rate.